1. Field of the Invention
The present invention relates to an infrared microscope analyzing a sample by irradiating infrared light onto the sample and measuring the spectra of the infrared light which passes through or reflects from the sample.
2. Description of the Related Art
In an infrared microscope, infrared light is projected on a sample, and the infrared light that has passed through the sample (or reflect from the sample surface) is spectrally measured, whereby the sample is analyzed. It is usually the case that a only limited area of the sample is required to be analyzed. In an analysis using the infrared microscope, an area caught within a field of view at each instance is generally a microscopic area of about 100 .mu.m to 1 mm. But according to circumstances, an analysis is carried out which specifically focuses on a much smaller area within the microscopic, a small foreign body, and the like discovered in the microscopic area. An infrared microscope generally has a field of view limitation mechanism composed of aperture plates and the like to analyze microscopic areas and bodies on a sample surface. If a field of view is limited suitably by the field of view limitation mechanism, noise and the like caused by an infrared light coming out of an undesired area or object is suppressed and a more accurate spectrum analysis can be carried out.
FIGS. 4(a) and (b) are a schematic diagrams of a main body around an aperture structure of a typical infrared microscope, wherein FIG. 4(a) shows a front view in which only the aperture structure 30 is shown in a vertical sectional view, and FIG. 4(b) shows a horizontal sectional view taken on line 4(b)-4(b) of FIG. 4(a).
A sample stand 41 is movable in a two dimensional plane of X-Y (furthermore, movable in the elevational direction, Z axis) by a sample stand driver not shown in the Figure. An objective optical system 42 comprising a lens, not shown in the Figure, and the like is disposed right above the sample stand 41. Above the objective optical system 42, the aperture structure 30 is disposed with its rotation axis 43 aligned with a central axis of the objective optical system 42. The aperture structure 30 includes an aperture holder 31 and four pieces of aperture plates 32-35. The aperture holder 31 is held in a pivotable condition about the rotation axis 43 in the main body of the infrared microscope, not shown in the Figure. A pair of opposite aperture plates 32, 34 among the four pieces of aperture plates 32-35 are slidably attached to the aperture holder 31 for movement on a straight line parallel to the X axis. The other pair of opposite aperture plates 33, 35 are also slidably attached to the aperture holder 31 for movement on a straight line parallel to the Y axis. An aperture driver, not shown in the Figure, is structured to move each aperture plate in each pair of aperture plates (32, 34 and 33, 35) in the opposite direction from each other in synchronization by the same distance. The aperture driver also rotates the whole the aperture holder 31 about the rotation axis 43 within a designated angle range. The sample stand driver and aperture driver may both be mechanically connected to manual operation of a knob and the like, respectively. Alternatively these drivers may be driven electrically by a motor and the like, respectively.
In case of analyzing a sample by the above infrared microscope, a sample 44 is placed on the sample stand 41 right under the objective optical system 42, then a visible light source 45 is turned on. The position of the sample stand 41 in the Z axis direction is properly adjusted and an enlarged image of the sample 44 is focused on a imaging surface of the aperture structure 30. The imaging surface is the contact surface between an upper aperture plate 33 and lower aperture plate 32 and 34. For example, as operators do visual observation of the enlarged image limited by an aperture 36, they adjust the position of each aperture plate 32-35, the rotation angle of the aperture holder 31, and the position of the sample stand 41 on the X-Y plane through proper operations so that the only desired part of the sample 44 can be observed through the aperture 36. When the above adjustments complete, the visible light source 45 is turned off and an infrared light source 46 is turned on, then the spectra analysis of the infrared light reflected from the surface of the sample 44 is carried out.
That is, as mentioned above, in the infrared microscope with the aperture 36 in the rectangular shape using the four pieces of aperture plates 32-35, the following adjustment work is generally necessary:
(1) determining a position (X, Y) of the aperture 36 relative to the sample 44 by properly changing the position of the sample stand 41 in X-Y plane; PA1 (2) determining each side length of the aperture 36 by adjusting the distance d1 between the first pair of aperture plates 32, 34 and the distance d2 between the second pair of aperture plates 33, 35; and PA1 (3) determining the angle of the aperture 36 by properly changing the rotation angle of the aperture holder 31 relative to the main body of the infrared microscope.
While the order of the above mentioned adjustment work of the aperture 36 can be changed suitably, in any case, operators are necessary to adjust as doing visual observation of the sample image whose field of view is limited by the aperture 36.
In the infrared microscope of the above mentioned structure since each aperture plate in each pair of aperture plates (32, 34 and 33, 35) are structured to move in the opposite direction from each other in synchronization by the same distance, the center of the aperture 36 ideally coincides to the rotation axis 43 of the aperture structure 30 (the rotation axis of the aperture holder 31). However, in practice, the center of aperture 36 may be off the rotation axis 43 due to the accuracy of finishing and assembling each part through the manufacturing process. Therefore, when the aperture holder 31 is rotated, the center of the sample image in the field of view of the aperture 36 changes after rotation. In an extreme case, the desired measurement point may be out of the field of view. Since a positional deviation depends on aged deterioration due to abrasion of parts and the like, even though there is no problem at the beginning of use, there is a possibility that the above problems will result from long-term use.